X-ray tube



Oct. 11, 193s. w H, MCCUIQDY 2,132,537

X-RAY TUBE Filed May 25, 1935 44 INVENTOR u /f fw/aw ATTORN EY Patented Oct. 11, 1.938 if X-RAY TUBE William H. McCurdy, Bloomfield, N. J., assignor,

by mesne assignments, to Westinghouse Electric and Manufacturing Company, East vPittsburgh, Pa., a corporation of Pennsylvania l Application May 25, 1935, serial No. 23,463

" '7 claims. (c1. 245g- 35) My invention relatesto X-ray tubes and par- It is'- accordingly Yan object of my present inllticularlyto what is known to the art as a double Vention to. provide an X-ray tube of the double focus tube. Y i focus type wherein an indication is given to an l In the utilization of an X-ray tube foruoroioperato'r which' is observable at a considerable scopic examinations it is essential in order to oby'distance that the smaller 'cathode is connected tain as much detail as possible that the focal spot to the source of cathode heating current and of small area. Thus the area of the tungsten the possibility of supplying an excessive current l target portion of the anode which isrimpinged by to the smaller cathode is eliminated as well as the `the electrons coming from the thermionic cathpreclusion of destruction of the small focal area odefis comparatively small with the result that of the anode. j l@ the generated X-rays are also confined to a small Another objectof my invention is the provision narrow beam producing desired detail and deni- `of an X-ray tube of the double focus type wheretion upon a fluorescent screen. Accordingly in -in either of the thermionic cathodes may be alorder tolproduce a small iine focus the discharge 'ternately connectedto a source of heating cur- UNi'reo stares "PATENT GFFICE current required for energization of the X-ray rent, and When the smaller cathode is so con- 15 tube `is relatively small. l nected means which are carried by the X-ray However, in the making of radiographic extubegives a visual indication observable at conposures it is necessary that a large focal spot be siderable,v distance that the smaller cathode is produced upon the surface of the anode with a Venergized and this means also prevents excesresultant increase in area of the emitted X-ray `sive heating current from being supplied to the 20 beam as well as the discharge current for the smaller cathode thus precluding an attendant in- X-ray tube. This has usually necessitated the crease 'inpdischarge current and a destruction .1 employment of two X-ray tubes with the normal ofthe small focal area of the anode.

lX-ray equipment, one tube being utilized for the Another 'object of my invention is the provision 25 making of iiuoroscopic examinations and the of ancX-ray tube ofthe double focus type having 25 "other for radiographic exposures. It has also a cathode terminal inthe form of a switch 1 been proposed in the prior art to provide a double which is operable to selectively connect each of focus tube wherein separate thermionic cathodes the thermionic cathodes to a source of heating :,:are utilized which are alternately energizable current, and a resistance is carried by the cath- ,3o` from an `appropriate source of heating current. `ode terminalwhich in one position of the switch Such cathodes are naturally of diiferent size and connects the resistance in series with the smaller design and may require heating current of differcathode and the sourceof heating current for ent magnitude in order to utilize maximum availthe purpose of giving a visual indication observa- `abledischarge current Vwithout destruction of the ble at a considerable distance from the tube that anode surface when changing from one focal area .the smaller cathode is energized and also to 35 tothe'other. i limit the current supplied to the small cathode The difference in cathode heating current to prevent-an increase in the discharge current necessitates two separate sources of different with a resulting destruction to the small focal magnitude each ofwhich are connected to the area of the anode. A,

40 respective cathodes As a low tension heating A further object of my present invention is 40 transformer is usually employed for supplying the provision of an X-ray tube of the double the cathode heating current andthe secondary -focus type having a cathode terminal constitutwinding thereof is so connected to the respective ing atwo position switch `for selectively connectcathodes as to supply the separate current tothe ing each of thethermionic cathodes to a source i respective cathodes it is by no meansnan unof heatingcurrent and wherein an incandescent 45 common occurrence for an operator to supply lamp is carried by the cathode terminal which in the smaller cathode with excessive current. This one position of theswitch is connected in series "may result in the cathode being disrupted but is with the smaller Cathode for the purpose of givmore apt to destroy the Small focal area of the `ing a Visual indication observable at Va distance 50\anode. Again while it has been proposed to prothat the smaller cathode is energized from the 50 `viole means whereby an operator can discern source of heating current and also to linut the which of the two cathodes is connected to the current supplied to the small cathode to prevent fheating source such indicator is difficult to oban increase in the discharge current with a reserve at an appreciable distance from the X-ray sulting destruction to the small focal area of the tube.. y y anode.` H `55 Fig. 2 is a sectional view of the cathode ter-r minal of the X-ray tube constructed in accordance with my present invention and taken on the line II-II of Fig. 1,

Fig. 3 is a sectional view of the cathode terrminal taken on the line III-III of Fig. 2,

Fig. 4 is a sectional view of the cathode terminal of my present invention taken on the line IV-IV of Fig. 3, and v Fig. 5 is a diagrammatic illustration of the electrical connections'of the X-ray tube cathodes :together with a schematic showing of various portions of thecathode terminal.

Referring now to the various figures in detail I have shown an X-ray. tube having the 'usual Vevacuated envelope 5. An anode electrode 6 is provided interiorly of the envelope in the usual manner and secured to the oppositely disposed reentrant portion of the envelope is 'a metallic shield 1 having elongated concave recesses 8 and .9 of. diiferent length and depth provided in the face of the shield which projects toward the anode vto form focusing cups, as can be morefappreciated by referance to Fig. 5. Disposed within the small-er recess 8 is a thermionic cathode in the form of a coiled tungsten filament vIll for producing a small focal areaand similarly within .the larger recess or 'focusing cup 9 is a longer coiled lamentary. cathode I2 which is spaced 'closer to the adjacent anode surface for producing a larger .focal area.

One end of each of the therminoic cathodes I and I2 is connected to the metallic shield 1 which latter is in turn connectedby a leading-in conductor I3 extending through the reentrant portion of the envelope vto`a contact terminal I4 provided on the exterior ofthe envelope. Lead- "ing-in conductors I and I6 likewise extend through the envelope and connect rthe remaining end of the respective cathodes Ill and l2 to contact terminalsIl and I8, respectively, disposed in juxtaposition to Vthe contact terminal Ie.-

vSlidably engaging the threey contact terminals I 4, I1 and I8 is-a cathode terminal which cornprises a block of rinsulating material I9 provided with recessed metallic sleeves 20, 22 and 23 (Fig. `2) establishing electrical 'contact with the respective terminals I4, I1 and I8. A retaining screw 25 has its head recessedwithin the face of the blockfl 9 adjacent theX-ray tube, which projectsbeyond the opposite face of the block I'9, and a metallic strap -25 interconnects the metallic sleeve and the screw 24, being held under the screw by a locknut or the like 26 and secured to the sleeve 20 in any suitable manner, such as by a scr-ew 21, thus forming a continuous electrical connection. A conventional lamp 'socket.28 is provided in the periphery of the block I9 which is adapted to threadedly receive a suitable incandescent lampforY 'a'purpose 'to be hereinafter more fully described.

A metallic strip 30, similar vto the strip 25, `is

screw 32, and extends a short distance ,across the surface of the block I9 where it is thenfangularly bent and protrudes within a recess 33 provided in the block I9 to thus form a spring contact for one terminal of the lamp 29. The socket 28, which is engaged by the shell of the lamp base, is connected by a suitable conductor 34 to an oiset spring contact member 35 secured to the surface of theblock I9, as can be more readily seen in Figs. 3 and 4.

' Likewise an oiset spring contact member 36 is connected, by means of a set screw or the like -31, to the metallic sleeve 23. For the purpose of enclosing the various spring contact members 35 and 36, as well as completing the switch elements for selectively connecting the cathodes l0 and I2 to a suitable source of heating current, suchas a low Vtension transformer 38, an insulating sleeve 39 fits loosely over the protruding end of the elongated screw 24 which sleeve has a portion of reduced diameter to form a shoulder 40.

A metallic disc 42 ts upon the larger diameter portion of the sleeve 39 and bearing against the periphery of this disc as well as the block I9 is a rotatable spider 43 having a pair of `radial arms 44 and 45 which alternately establish wiping engagement with either of 'the spring contact members, 35 and 36 depending upon the direction of rotation of the spider. A pin 46 protrudes from the face of the block I9 which is contacted by either of thev radial arms 44 and 45 thus limiting maximum rotation of the spider in either direction to approximately 30.

A metallic spring plate 41 rests against the shoulder 49 of the sleeve 39 and presses against the member 52 to hold the spider 43 in place and in order to also maintain the spring plate 41 in place a further insulating block 48 is carried by the screw V2li. The flat surfaces of this insulating block 48 are provided with metallic plates 49 and 50 and interposed between the plate 50 and .the spring plate 41 is a metallic spring washer 52. Similarly a metallic spring washer 53 bears 'against the'metallic surface of the block 1&8 and the entire assembly is held inplace through the Ymedium of a'nut AEll engaging the end of the elongated screw-24. The metallic plates 49 and V5I] are flared inwardly to form suitable recesses between the adjacent spring washers 52 and 53. respectively, to thus form a receptacle for the engagement -of a plug 55 connected to the cathode heating source `or transformer 38. Due to Ythe -the elongated screw, 24 and sleeve 39 with the plug 55 thus following rotation of the block'll k5 to prevent straining -or tangling of the conductors from the'low voltage transformer.`

It will thus be observed that one conductor 56 ,extending from the transformer '38 is connected directly to `theplate y49 and spring washer 53fby the engagement of one of the prongs of the plug 55. The nut54 bearing against this washer 53 *thus transmits the current to the elongated bolt V215,and the interconnecting metallic strap in turn transmits this Ycurrent to the recessed meta'llic sleeve*20,'which is engagedv by the contact terminal i'4l, and consequently to the cathode connected. The remaining conductor 51'extendingfrom` the source'or transformer 38 is similarly connected by the other prong of the "plug 55 55 to the plate 5ll'"an'dfspringl washer* 52 which latter' being" in contact withthe metallic spring plate 41 thus transmits the current to the metal- *smaller cathode l0 by the Vconductor `I5.` `Accordingly'with thefswitchfin the position shown in Figs. 3 and 4 with the radial arm 45 ofthe spider 43 in contact with the terminal 35 not only is the 'smaller cathode I0 connected to the source of Aheatingcurrento'r transformer 38 'for theproduction of Va small focal spotV but the incandescent lamp 29is connected in a series circuit with this'cathode I0 and the source38. In- `asmuchas the lamp naturally has inherent ohmic resistance it functions to limit the magnitude of the current supplied to the small cathode I0 and thus precludes the possibility of excessive heating current,` suchV as all that is available from the transformer 38, being inadvertently supplied to the'small cathode.` This naturally would otherwise cause an increase in the discharge current when the tube is energized with resulting destruction to the small focal area of the anode. Moreover, the incandescent lamp when illuminated by operationof thelswitch gives a visual indication observable by an operator at a considerable distancefrom the X-ray tube that the small cathode isenergized thus showing the same is functioningandproducingj the desired focal spot for the appropriate examination. 1

` Ai still further advantageous feature in the utilization ofthe incandescenty lamp 29 resides in the `fact that the energy consumed thereby is readily dissipated inl `the 'form of heat to the surrounding atmosphere `thus preventing such heat `frornotherwise causing deterioration of the insulating material of which the greater portion ofthe cathode terminal is composed. v

The spider 43 is provided on its outer periphery with a'metallic ring 58 having indicium thereon "as can be seen from Fig. l, which aligns with an arrow 59 provided 4on, the periphery of the block |9. Accordingly when it is desired to alter the focal spotfor theQpurpose of making a radiographicexposure the switch or spider 43 is` rotatedlin.alcounter-cloclgwise direction, as viewed from Fig. 4; until thelindicia large aligns with the arrow 59 shown in Fig. 1. This will then move the radial arm 45 out of contact with the offset spring contact terminal 35 against the pin 4B and at the same time the radial arm 44 will be moved away from this pin 46 into engagement with the offset spring contact terminal 36 as shown by the dotted lines in Fig. 4.

The current through the incandescent lamp 29 and the smaller cathode l0 will thus be interrupted and in lieu thereof current will then be supplied from the spider 43 to the spring contact 36 and recessed metallic sleeve 23, and through the contact terminal I8 and conductor I6 to the other end of the larger cathode l2. In this position of the switch the maximum current from the heating source is therefore supplied directly to the larger of the thermionic cathodes with the result that when the X-ray tube is energized by high potential, the ensuing discharge current will be higher and due to the design of this larger cathode I2together with the focusing cup 9 a larger focal spot is produced upon the anode-surface as required for this particulartype of examination.

Itis also frequently desirable to limit the current supplied by the source to either of the cathodes and that the same be adjustable from time to time. In this event a variable resistance 60 is provided on the conventional control stand which usually encases the cathode heating transformer and is permanently connected in series with the primary winding of the heating transformer 38 and with either of the supply conductors leading from the usualcommercial source of electrical energy.

It thus becomes obvious to those skilled in the art that I have provided an X-ray tube of the double focus type wherein the same is provided with means forming a cathode terminal, which are operable to alternately connect either of the thermionic cathodes to a source of heating current. Moreover an incandescent lamp is provided which functions for the dual purpose of giving a Visual indication observableat a considerable distance from the machine that the small cathode is energized and which also precludesexcessive current from being inadvertently supplied to the-cathode for producing the small focal spotwith the result that the discharge current is prevented from increasing and causing a destruction of the small focal area of the anode. i I

Although I have shown one specific embodiment of my present invention I do not desire to belimited thereto as various other modifications thereof may be made without departing from the spirit and scope of the appended claims.

What is claimed:

1. An X-ray tube comprising an evacuated envelope.- an anode electrode in said envelope, a pair of thermionic cathodes adapted to be heated to incandescence independently of each other disposed in said envelope for producing dissimilar focal spots, means surrounding each of said cathodes for focusing a discharge therefrom upon different size areas of the surface of said anode, means Voperable to selectively connect each of said cathodes to a source of heating current, and means operable upon operation of said last mentioned means to give-a visual indication observable at considerable distance that current is supplied to said cathode which produces the smaller focal spot and to simultaneously limit the current supplied t'o such cathode to prevent a resulting increase in discharge current supplied `to saidV X-raytube with `attendant destruction of the-small focal area of said anode.

2. An X-ray tube comprising an evacuated envelope, an anode electrode in said envelope, a pr of thermionic cathodes adapted to be heated to incandescence independently of each other disposed in said envelope for producing dissimilar focal spots, means surrounding each of said cathodes for focusing a discharge therefrom upon different size areas of the surface of said anode, means carried by said X-ray tube and operable to selectively connect each of said cathodes to a source of heating current, and means carried by said last mentioned means and operable upon operation thereof to give a visual indication observable at considerable distance from said tube that current is supplied to said cathode which producesthe smaller focal spot and for simultaneously limiting the current jsupplied to such cathode to prevent a resulting increase in X-ray tube discharge current with attendant destruction of .the small focal areafof said anode. f

3. An X-ray tube comprising "an, evacuated envelope, an anode electrodeA in `said envelope, a pair of thermionic cathodes adapted to be heated to incandescence independently of each other disposed in said envelope for producing dissimilar focal spots, means surrounding each of` said cathodes for focusing a discharge therefrom upon different size areas of the surface of said anode, and means carried by said tube operative to` selectively connectV each vof said cathodes to a source of heating current and for giving a visual indication observable at considerable distance'from vsaid tube that current is. supplied to said cathode which produces the smaller focal spotin one position of said lastrmentioned means' as Well as for simultaneously limiting Ythe k,current supplied Y to the smaller focal spot producing `cathode when connected to said source ofk heating current to prevent an increase in the X-ray tube discharge current with attendant destruction of the focal area of said anode. v Y Y 4. An X-ray tube comprising an :evacuated envelope, an anode electrode in said envelope, a pair of thermionic cathodes `adapted to be heated to incandescence independentlylof each other'disposed in said envelope for producing ldissimilar focal spots, means surrounding each of said cathodes for focusing a discharge therefromupon different size areas of the surface Yof said anode, and a cathode terminal for said X-ray tube including means operablelto selectively connect each of said cathodes to a source of heating current and means loperable upon operationl of said last mentioned means in one position to give a visual indication observable at a considerable distance from said X-ray tubethat current is supplied to said-cathode which produces the smaller focal spot and to simultaneouslylimit the current supplied to such cathode, to prevent an increase in the X-ray tube discharge current with attendant destruction of therfocal area of said anode. y

5. An X-ray tube comprisingY an evacuated envelope, an anode-electrode in said envelope, a pair of thermionic cathodes adaptedlto be heated to incandescence independently of each other'disposed in said envelope ,for producing dissimilar focal spots, means surrounding each of said cathodes for focusing a discharge therefromjupon different size areask of the surface of said anode, a switch-carried by said X-,ray tube and roperable to selectively connect veach `vof said cathodes to a source of heating current, and a device adapted to be connected to one of saidjcathodes and -the jsource vof l1eating icurrent by operation of said switch in one position to give a visual indication observable-at aY considerable distance from said X-ray tube that current is supplied to the smaller focal spot producing cathode and Asaid device being simultaneously operable to limitv the current supplied to such cathode to prevent an increase in the vX-ray tube discharge current with attendant ydestruction vof the focal varea of said anode. 1

V,6. An X-ray tube comprising an evacuated envelope, an anode electrode in said envelope, a pair of thermionic cathodes adapted to be heated to incandescence independently of each other disposed in said envelope, means surrounding each of said cathodes for focusing a discharge therefrom upon different size areas of vthe surface of said anode, a switch carried by said X-ray tube and operable to selectively connect each of said cathodes to a source ofiheating current, and an incandescent lamp lcarried by said switch and adapted to be connected 'to one ofsaid cathodes and the source of heating currentxby operation of said switch in-v one position for the purpose of giving a visualuindic'ation observable Vat a considerable distance from said X-ray tube that the current supplied toone of said cathodes is so limited and to simultaneously limit the current supplied tokone of said cathodes to prevent an increase in the X-ray tube discharge current With attendantdestruction of the focalarea of said anode. ,Y t ,s A Y I VAn X-ray tube comprising an evacuated envelope,- an anode electrode in ksaid envelope, a pair of thermionic cathodes adapted to be heated to incandescence independently of each other disposed in said envelope, Vvone of said cathodes beingof materially shorter-length and disposed further from said anode than the remaining cathode, means surrounding each of said cathodes for focusing a discharge therefrom uponfdiierent size areas of the surface/of said v anode, and meansfc'arried by saiLX-rayl tube operable to selectively connect each of said cathodes Yto a source of heating current and'. operable inone position to interposea current limiting device between said source of heating current andthe cathode of Vshorter length to giveavisualindication observableat a considerable distance from said X-ray tube that the cathode of shorter length is connected to saidsource of heating current and for simultaneously preventing excessive heating current kbeing supplied 'to the cathode of shorter length with* an increase in X-ray tube discharge cur-'rent and destructionY of the small focal area of said anode producedby said shorter cathode.Y 7

' i WILLIAM I-I.' MCCURDY. 

